Karen Sievwright believes in a well-rounded, healthy diet for her three children. But she’s also convinced their daily dose of multivitamins gives them a special advantage.

While other children typically get several colds a year, Ms. Sievwright says her kids breeze through only one or two shorter-lasting viruses, and her oldest son seems to actually heal himself when he gets an ear infection.

“They bounce back much faster,” says the nutrition and fitness coach from Stony Plain, Alta. “I feel it helps the body to do its job.”

Ms. Sievright’s belief in the power of supplements is far from unusual: An estimated 14 million Canadians — children and adults — take vitamins, contributing to sales of about $370 million a year. And those numbers are climbing steadily, according to the market-research firm Euromonitor International.

But a number of recent studies suggest that while our belief in the power of vitamins keeps growing, evidence that they do anything to boost the health of people who don’t suffer from vitamin deficiencies is shrinking. At a certain point, some might actually do harm.

“Enough is enough. Stop wasting money on vitamin and mineral supplements,” one major medical journal chided in one unusually blunt editorial.

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How did we get here?

In her new book Vitamania: Our Obsessive Quest For Nutritional Perfection, U.S. journalist Catherine Price traces the fascinating history of the vitamin.

[np_storybar title=”How do vitamins work? An excerpt from Vitamania: Our Obsessive Quest for Nutritional Perfection” link=”http://news.nationalpost.com/2015/02/28/vitamania-excerpt/”%5D One thing that’s undoubtedly happening when you eat an apple (or any other natural food, for that matter) is synergy, the phenomenon in which substances work differently when they’re together than when they’re on their own — the vitamin C in a Red Delicious, for example, may not act the same way in isolation as it does when it’s surrounded by an apple’s other compounds.

It’s a story that likely began on the ships that have crisscrossed the world’s oceans for centuries, keeping their crews at sea for weeks or months on end. Until the mid-1800s, the mysterious disease known as scurvy took a tremendous toll, killing more than two million seamen, beginning with symptoms that included sore gums and loose teeth.

It wasn’t until a naval doctor in 1747 conducted possibly the world’s first clinical trial — putting groups of sailors on different “treatments” and seeing how they fared — that citrus fruit was confirmed as a preventive. It worked remarkably, though no one knew at the time about vitamin C.

It was the early 20th century before researchers pinpointed the underlying trigger for such illnesses — which included now obscure diseases such as beriberi and pellagra — identifying 13 compounds crucial to regulating metabolic activity and other cellular processes, mostly obtained by humans from food — and a major problem if missing.

“In a state of true deficiency, if you take a vitamin, it can be miraculous,” says Ms. Price in an interview this week.

In a state of true deficiency, if you take a vitamin, it can be miraculous

Consumers have long been dazzled by vitamins’ “magical-seeming powers,” she says, citing the squirt of vitamin A that restores sight to blind, malnourished children in parts of Africa.

But our love affair with vitamins seems built on something more: the notion that adding to our minimum required intake will lead to added benefits — including everything from mood enhancement to longevity.

In the lead-up to America’s entry into the Second World War, for instance, some doctors and media seized on one of the newly discovered substances — thiamin, or vitamin B1 — as a “morale” vitamin that could steady nerves and add “zest for living” in the battle to come.

The discovery of vitamins was also a marketing goldmine from the start. As Ms. Price writes, in the 1930s, it led to vastly increased sales of products like iceberg lettuce, which contains vitamins A and K, though little else of value.

Windsor Star-Rob Gurdebeke

Ironically, the reason why the nutrients were missing from many diets stems from man-made manipulation of some grocery staples. The milling that produces white flour and white rice and sterilization that makes packaged products safe removes the very parts of those foods that contain life-sustaining vitamins.

The solution? Synthetically produced versions are routinely added back in to the nutrient-stripped food, from bread to low-fat milk and fruit drinks.

The appeal of vitamins has likely been enhanced by the scientific-sounding yet pleasing name devised by Polish biochemist Casimir Funk, vita, which is Latin for life, says Ms. Price.

Regardless, the consumption of vitamin supplements — taken on top of those added to a vast range of foods — has grown largely unabated.

In addition to all but eliminating — in the industrialized world, at least — vitamin-deficiency diseases, this has led to some real triumphs. Fortifying flour with folic acid, for instance, and encouraging pregnant women to take folic-acid pills, has dramatically reduced the rate of devastating neural-tube birth defects, which leave babies with conditions like spina bifida.

Vitamin D is considered an important supplement for protecting women’s bone health, while a slew of promising but not definitive studies has suggested it could protect people from a host of other illnesses.

A spokesman for the country’s main natural-health product trade group dismisses assertions that supplements achieve little good. She points to evidence that many Canadians do not absorb enough essential vitamins through the foods they eat.

Supplements act as a “bridge,” says Helen Long, president of the Canadian Health Food Association. “These are precisely the people who stand to benefit from natural health products,” she said in an emailed statement.

The problem is how deeply we invest in the power of supplements to make us healthy. Vitamin-C continues to be touted as a cancer cure, despite a lack of solid scientific backing for the idea. The same goes for claims that vitamins might protect adults against heart disease, or reduce the risk of death for those who have it.

Concerns are also surfacing around the safety of consuming too many supplements. Rima Rozen is a McGill University geneticist investigating the dangers of excessive amounts of folic acid. She and her colleagues have just published the latest in a string of studies looking at the impact of high doses – finding that 10 times the recommended daily intake of the vitamin, often the dose doctors recommend for pregnant women, causes liver damage in mice.

“If you have too much or too little, very often you disturb the processes in the cell,” says Prof. Rozen. And when people are taking high-dose supplements, on top of vitamins added to foods, she adds, “you really have no idea how much you’re ingesting.”

Ran Goldman, a pediatrics professor at the University of British Columbia who has studied the interaction between supplements and drugs in emergency-department patients, has more pointed criticisms. “As a society we have been captured by a well-oiled public relations machine to believe in the benefits of consuming more and more vitamins,” he says. “Vitamins have become the panacea of the 21st century.”

So how do we know whether we’re taking the right vitamin, or whether taking a vitamin is the right thing to do at all?

Health Canada licenses 4,400 different vitamin products under its natural-health-product system, including 570 varieties of multivitamin products alone. Government-approved labels indicate that they are “a factor in the maintenance of good health.”

Health Canada’s publicly available assessments of vitamins are not quite comprehensive about possible risks. The label, or product monograph, for vitamin E, for instance, cites more than 130 journal papers, but leaves out a major 2011 report that suggested an increased risk of prostate cancer among those who took E supplements. Nor is that possible risk mentioned under the “cautions and warnings” heading.

The monograph for vitamin A lists nothing under “cautions and warnings,” though some, inconclusive, studies have found links between very high doses of the nutrient and increased fracture risk of birth defects.

But Eric Morissette, a Health Canada spokesman, said vitamins, like other natural health products, are safe and effective when used according to government-approved recommendations.

“Vitamin products are available on the market to ensure that the consumer, no matter his or her nutritional status, has ready access to a range of alternatives for maintaining and improving their health,” he said.

In Alberta, Ms. Sievwright says she agrees with warnings about depending too much on vitamin supplements — but only to a point.

“If the only thing you’re relying on is a vitamin out of the bottle to make you healthy, you’re missing the whole concept,” she says. “There is no magic pill that is going to do that for you.”

Even McGill’s Prof Rozen says she takes multivitamins as a back-up to her diet.